Chemically modified and conjugated antimicrobial peptides against superbugs

Antibacterial effect of synthetic ultra-short lipopeptide on Streptococcus agalactiae and its active on bacterial mastitis in mice

Streptococcus agalactiae mastitis is one of the significant threats to the milk industry. The traditional antibiotic treatment method is easy to cause the emergence of resistant strains, and the problem of drug residue is increasingly severe. In this study, we designed and synthesized five lipopeptides. The antibacterial activity of different molecular structure lipopeptides against Streptococcus agalactiae was detected. Furthermore, the mouse mastitis model was established using Streptococcus agalactiae. The lipopeptides with better antibacterial effect were selected for the treatment experiment to evaluate the application value in the treatment of mastitis. The results showed that 4 of the synthesized lipopeptides had specific antibacterial activity. SLP3 and SLP4 have an excellent antibacterial effect and can treat murine mastitis caused by Streptococcus agalactiae infection within the safe concentration range. The results of this study can provide an excellent experimental basis for new antibiotics and clinical application in the treatment of dairy cow mastitis.

Enhancing proline-rich antimicrobial peptide action by homodimerization: influence of bifunctional linker

Antimicrobial peptides (AMPs) are host defense peptides, and unlike conventional antibiotics, they possess potent broad spectrum activities and, induce little or no antimicrobial resistance. They are attractive lead molecules for rational development to improve their therapeutic index. Our current studies examined dimerization of the de novo designed proline-rich AMP (PrAMP), Chex1-Arg20 hydrazide, via C-terminal thiol addition to a series of bifunctional benzene or phenyl tethers to determine the effect of orientation of the peptides and linker length on antimicrobial activity. Antibacterial assays confirmed that dimerization per se significantly enhances Chex1-Arg20 hydrazide action. Greatest advantage was conferred using perfluoroaromatic linkers (tetrafluorobenzene and octofluorobiphenyl) with the resulting dimeric peptides 6 and 7 exhibiting potent action against Gram-negative bacteria, especially the World Health Organization's critical priority-listed multidrug-resistant (MDR)/extensively drug-resistant (XDR) Acinetobacter baumannii as well as preformed biofilms. Mode of action studies indicated these lead PrAMPs can interact with both outer and inner bacterial membranes to affect the membrane potential and stress response. Additionally, 6 and 7 possess potent immunomodulatory activity and neutralise inflammation via nitric oxide production in macrophages. Molecular dynamics simulations of adsorption and permeation mechanisms of the PrAMP on a mixed lipid membrane bilayer showed that a rigid, planar tethered dimer orientation, together with the presence of fluorine atoms that provide increased bacterial membrane interaction, is critical for enhanced dimer activity. These findings highlight the advantages of use of such bifunctional tethers to produce first-in-class, potent PrAMP dimers against MDR/XDR bacterial infections.

Homodimerization of a proline-rich antimicrobial peptide via bioconjugation to perfluoroaromatic linkers confers increased antimicrobial, antibiofilm and immunomodulatory activity. The dimers are promising new therapeutic leads against WHO priority multidrug resistant bacteria.

Discovery and Characterization of a New Crustin Antimicrobial Peptide from Amphibalanus amphitrite

Crustins are an antimicrobial peptide (AMP) family that plays an important role in innate immunity in crustaceans. It is important to discover new AMPs from natural sources to expand the current database. Here, we identified and characterized a new crustin family member, named AaCrus1, from Amphibalanus amphitrite. AaCrus1 shares high identity (48.10%) with PvCrus, a Type I crustin of Penaeus vannamei that possesses a whey acidic protein (WAP) domain. AaCrus1 contains 237 amino acids and eight cysteine residues forming conserved ‘four-disulfide core’ structure. Our recombinant AaCrus1 (rAaCrus 1) could inhibit the growth of two Gram-positive bacteria (Staphylococcus aureus, Bacillus sp. T2) and four Gram-negative bacteria (Vibrio parahaemolyticus, Vibrio harveyi, Vibrio anguillarum, Vibrio alginolyticus) with a minimum inhibitory concentration of 3.5–28 μM. It can further induce agglutination of both Gram-positive and Gram-negative bacteria. rAaCrus1 can bind to bacteria and damage bacterial cell membranes. Furthermore, rAaCrus1 disrupted biofilm development of S. aureus and V. parahaemolyticus. Our discovery and characterization of this new crustin can be further optimized as a good alternative to antibiotics.

Antimicrobial-wound healing peptides: Dual-function molecules for the treatment of skin injuries

Chronic non-healing wounds caused by microbial infections extend the necessity for hospital care and constitute a public health problem and a great financial burden. Classic therapies include a wide range of approaches, from wound debridement to vascular surgery. Antimicrobial peptides (AMPs) are a preserved trait of the innate immune response among different animal species, with known effects on the immune system and microorganisms. Thus, AMPs may represent promising candidates for the treatment of chronic wounds with dual functionality in two of the main agents that lead to this condition, proliferation of microorganisms and uncontrolled inflammation. Here, our goal is to critically review AMPs with wound healing properties. We strongly believe that these dual-function peptides alone, or in combination with other wound healing strategies, constitute an underexplored field that researchers can take advantage of.

Allosteric Inhibition of Acinetobacter baumannii ATP Phosphoribosyltransferase by Protein:Dipeptide and Protein:Protein Interactions

ATP phosphoribosyltransferase (ATPPRT) catalyzes the first step of histidine biosynthesis in bacteria, namely, the condensation of ATP and 5-phospho-α-d-ribosyl-1-pyrophosphate (PRPP) to generate N¹-(5-phospho-β-d-ribosyl)-ATP (PRATP) and pyrophosphate. Catalytic (HisG_S) and regulatory (HisZ) subunits assemble in a hetero-octamer where HisZ activates HisG_S and mediates allosteric inhibition by histidine. In Acinetobacter baumannnii, HisG_S is necessary for the bacterium to persist in the lung during pneumonia. Inhibition of ATPPRT is thus a promising strategy for specific antibiotic development. Here, A. baumannii ATPPRT is shown to follow a rapid equilibrium random kinetic mechanism, unlike any other ATPPRT. Histidine noncompetitively inhibits ATPPRT. Binding kinetics indicates histidine binds to free ATPPRT and to ATPPRT:PRPP and ATPPRT:ATP binary complexes with similar affinity following a two-step binding mechanism, but with distinct kinetic partition of the initial enzyme:inhibitor complex. The dipeptide histidine-proline inhibits ATPPRT competitively and likely uncompetitively, respectively, against PRPP and ATP. Rapid kinetics analysis shows His-Pro binds to the ATPPRT:ATP complex via a two-step binding mechanism. A related HisZ that shares 43% sequence identity with A. baumannii HisZ is a tight-binding allosteric inhibitor of A. baumannii HisG_S. These findings lay the foundation for inhibitor design against A. baumannii ATPPRT.

Self-Deliverable Peptide-Mediated and Reactive-Oxygen-Species-Amplified Therapeutic Nanoplatform for Highly Effective Bacterial Inhibition

An "antibiotic-free strategy" provides a viable option to address bacterial infections, especially for the "superbug" challenge. However, the undesirable antibacterial activity of antibiotic-free agents hinders their practical applications. In this study, we developed a combination antibacterial strategy of coupling peptide-drug therapy with chemodynamic therapy (CDT) to achieve the effective bacterial inhibition. An amphiphilic oligopeptide (LAOOH-OPA) containing a therapeutic unit of D(KLAK)2 peptide and a hydrophobic linoleic acid hydroperoxide (LAHP) was designed. The positively charged D(KLAK)2 peptide with an α-helical conformation enabled rapid binding with microbial cells via electrostatic interaction and subsequent membrane insertion to deactivate the bacterial membrane. When triggered by Fe2+, moreover, LAHP could generate singlet oxygen (1O2) to elicit lipid bilayer leakage for enhanced bacteria inhibition. In vitro assays demonstrated that the combination strategy possessed excellent antimicrobial activity not only merely toward susceptible strains (Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli) but also toward methicillin-resistant Staphylococcus aureus (MRSA). On the mouse skin abscess model induced by S. aureus, self-assembled LAOOH-OPA exhibited a more significant bacteria reduction (1.4 log10 reduction) in the bioburden compared to that of the standard vancomycin (0.9 log10 reduction) without apparent systemic side effects. This combination antibacterial strategy shows great potential for effective bacterial inhibition.

Indolicidin revisited: biological activity, potential applications and perspectives of an antimicrobial peptide not yet fully explored

The emergence of multidrug-resistant bacteria, viruses and tumors is a serious threat to public health. Among natural peptides, indolicidin, a 13-residue peptide belonging to the cathelicidin family, deserves special attention. Indolicidin has a broad spectrum of biological activity and is active against a wide range of targets, such as bacteria (Gram+  and Gram-), fungi and viruses. Here, we review the most important features of the biological activity, potential applications and perspectives of indolicidin and its analogs. Although not yet approved for commercialization, this peptide has great potential to be applied in different areas, including the medical, biomedical, food industry and other unexplored areas. To achieve this goal, a multidisciplinary team of researchers must work together to fine tune peptides that overall lead to novel analogs and formulations to combat existing and possibly future diseases.

Novel Arginine End-Tagging Antimicrobial Peptides to Combat Multidrug-Resistant Bacteria

The emergence of multidrug-resistant microorganisms has been termed one of the most common global health threats, emphasizing the discovery of new antibacterial agents. To address this issue, we engineered peptides harboring "RWWWR" as a central motif plus arginine (R) end-tagging and then tested them in vitro and in vivo. Our results demonstrate that Pep 6, one of the engineered peptides, shows great potential in combating Escherichia coli bacteremia and the Staphylococcus aureus skin burn infection model, which induces a 62-90% reduction in bacterial burden. Remarkably, after long serial passages of S. aureus and E. coli for 30 days, Pep 6 is still highly efficient in killing pathogens, compared with 64- and 128-fold increase in minimal inhibitory concentrations (MICs) for vancomycin and polymyxin B, respectively. We also found that Pep 6 exhibited robust biofilm-inhibiting activity and eliminated 61.33% of the mature methicillin-resistant Staphylococcus aureus (MRSA) biofilm with concentration in the MIC level. These results suggest that the RWWWR motif and binding of arginine end-tagging could be harnessed as a new agent for combating multidrug-resistant bacteria.

The Potential of Modified and Multimeric Antimicrobial Peptide Materials as Superbug Killers

Antimicrobial peptides (AMPs) are found in nearly all living organisms, show broad spectrum antibacterial activity, and can modulate the immune system. Furthermore, they have a very low level of resistance induction in bacteria, which makes them an ideal target for drug development and for targeting multi-drug resistant bacteria 'Superbugs'. Despite this promise, AMP therapeutic use is hampered as typically they are toxic to mammalian cells, less active under physiological conditions and are susceptible to proteolytic degradation. Research has focused on addressing these limitations by modifying natural AMP sequences by including e.g., d-amino acids and N-terminal and amino acid side chain modifications to alter structure, hydrophobicity, amphipathicity, and charge of the AMP to improve antimicrobial activity and specificity and at the same time reduce mammalian cell toxicity. Recently, multimerisation (dimers, oligomer conjugates, dendrimers, polymers and self-assembly) of natural and modified AMPs has further been used to address these limitations and has created compounds that have improved activity and biocompatibility compared to their linear counterparts. This review investigates how modifying and multimerising AMPs impacts their activity against bacteria in planktonic and biofilm states of growth.

Antimicrobial peptides, conventional antibiotics, and their synergistic utility for the treatment of drug-resistant infections

Antimicrobial peptides (AMPs), also known as host defense peptides (HDPs), are important effector immune defense molecules in multicellular organisms. AMPs exert their antimicrobial activities through several mechanisms; thus far, induction of drug resistance through AMPs has been regarded as unlikely. Therefore, they have great potential as new generation antimicrobial agents. To date, more than 30 AMP-related drugs are in the clinical trial phase. In recent years, studies show that some AMPs and conventional antibiotics have synergistic effects. The combined use of AMPs and antibiotics can kill drug-resistant pathogens, prevent drug resistance, and significantly improve the therapeutic effects of antibiotics. In this review, we discuss the progress in synergistic studies on AMPs and conventional antibiotics. An overview of the current understanding of the functional scope of AMPs, ongoing clinical trials, and challenges in the development processes are also presented.

Antimicrobial peptide-based materials: opportunities and challenges

The multifunctional properties of antimicrobial peptides (AMPs) make them attractive candidates for the treatment of various diseases. AMPs are considered alternatives to antibiotics due to the rising number of multidrug-resistant...

Grafting MSI-78A onto chitosan microspheres enhances its antimicrobial activity

MSI-78A (Pexiganan A) is one of the few antimicrobial peptides (AMPs) able to kill Helicobacter pylori, a pathogenic bacterium that colonizes the gastric mucosa of half of the world's population. Antibiotics fail in 20-40% of H. pylori-infected patients, reinforcing the need for alternative treatments. Herein, a bioengineered approach was developed. MSI-78A with a C-terminal cysteine was grafted onto chitosan microspheres (AMP-ChMic) by thiol-maleimide (Michael-addition) chemistry using a long heterobifunctional spacer (NHS-PEG₁₁₃-MAL). Microspheres with ∼4 µm diameter (near H. pylori length) and stable at low pH were produced by spray drying using a chitosan solution with an incomplete genipin crosslinking. A 3 × 10^-5 µg AMP/microsphere grafting was estimated/confirmed by UV/Vis and FTIR spectroscopies. AMP-ChMic were bactericidal against H. pylori J99 (highly pathogenic human strain) at lower concentrations than the free peptide (∼277 µg grafted MSI-78A-SH/mL vs 512 µg free MSI-78A-SH/mL), even after pre-incubation in simulated gastric conditions with pepsin. AMP-ChMic killed H. pylori by membrane destabilization and cytoplasm release in a ratio of ∼10 bacteria/microsphere. This can be attributed to H. pylori attraction to chitosan, facilitating the interaction of grafted AMP with bacterium membrane. Overall, it was demonstrated that the peptide-microsphere conjugation chemistry did not compromise the MSI-78A antimicrobial activity, instead it boosted its bactericidal performance against H. pylori. STATEMENT OF SIGNIFICANCE: Half of the world's population is infected with Helicobacter pylori, a gastric bacterium that is responsible for 90% of non-cardia gastric cancers. Therefore, H. pylori eradication is now advocated in all infected individuals. However, available antibiotic therapies fail in up to 40% patients. Antimicrobial peptides (AMPs) are appealing alternatives to antibiotics, but their high susceptibility in vivo limits their clinical translation. AMP immobilization onto biomaterials surface will overcome this problem. Herein, we demonstrate that immobilization of MSI-78A (one of the few AMPs with activity against H. pylori) onto chitosan microspheres (AMP-ChMic) enhances its anti-H. pylori activity even at acidic pH (gastric settings). These results highlight the strong potential of AMP-ChMic as an antibiotic alternative for H. pylori eradication.

Multiple roles of ribosomal antimicrobial peptides in tackling global antimicrobial resistance

In the last century, conventional antibiotics have played a significant role in global healthcare. Antibiotics support the body in controlling bacterial infection and simultaneously increase the tendency of drug resistance. Consequently, there is a severe concern regarding the regression of the antibiotic era. Despite the use of antibiotics, host defence systems are vital in fighting infectious diseases. In fact, the expression of ribosomal antimicrobial peptides (AMPs) has been crucial in the evolution of innate host defences and has been irreplaceable to date. Therefore, this valuable source is considered to have great potential in tackling the antimicrobial resistance (AMR) crisis. Furthermore, the possibility of bacterial resistance to AMPs has been intensively investigated. Here, we summarize all aspects related to the multiple applications of ribosomal AMPs and their derivatives in combating AMR.

Peptide Multimerization as Leads for Therapeutic Development

Multimerization of peptide structures has been a logical evolution in their development as potential therapeutic molecules. The multivalent properties of these assemblies have attracted much attention from researchers in the past and the development of more complex branching dendrimeric structures, with a wide array of biocompatible building blocks is revealing previously unseen properties and activities. These branching multimer and dendrimer structures can induce greater effect on cellular targets than monomeric forms and act as potent antimicrobials, potential vaccine alternatives and promising candidates in biomedical imaging and drug delivery applications. This review aims to outline the chemical synthetic innovations for the development of these highly complex structures and highlight the extensive capabilities of these molecules to rival those of natural biomolecules.

Facile Biofilm Penetration of Cationic Liposomes Loaded with DNase I/Proteinase K to Eradicate Cutibacterium acnes for Treating Cutaneous and Catheter Infections

Background

The biofilm produced by Cutibacterium acnes is a major infection threat for skin and implanted catheters. Nanoparticles provide a new approach to eradicate biofilms. The present study evaluated the capability of cationic liposomes loaded with DNase I (DNS) and proteinase K (PK) to remove preformed C. acnes biofilms.

Methods

DNS and PK were able to target and disassemble the biofilm by degrading extracellular polymer substances (EPS). Soyaethyl morpholinium ethosulfate (SME) was used to render a positive charge and enhance the antibacterial activity of the liposomes.

Results

The cationic liposomes containing enzymes yielded monodisperse nanovesicles ranging between 95 and 150 nm. The entrapment efficiency of the enzymes in the liposomes achieved a value of 67–83%. All liposomal formulations suppressed planktonic C. acnes growth at a minimum inhibitory concentration (MIC) equal to the free SME in the solution. The enzyme in the liposomal form inhibited biofilm growth much better than that in the free form, with the dual enzyme-loaded liposomes demonstrating the greatest inhibition of 54% based on a crystal violet assay. The biofilm-related virulence genes PA380 and PA1035 were downregulated by the combined enzymes in the liposomes but not the individual DNS or PK. Scanning electron microscopy (SEM) and confocal microscopy displayed reduced C. acnes aggregates and biofilm thickness by the liposomal system. The liposomes could penetrate through about 85% of the biofilm thickness. The in vitro pig skin permeation also showed a facile delivery of liposomes into the epidermis, deeper skin strata, and hair follicles. The liposomes exhibited potent activity to eliminate C. acnes colonization in mouse skin and catheters in vivo. The colony-forming units (CFUs) in the catheter treated with the liposomes were reduced by 2 logs compared to the untreated control.

Conclusion

The data suggested a safe application of the enzyme-loaded cationic liposomes as antibacterial and antibiofilm agents.

ElyC and Cyclic Enterobacterial Common Antigen Regulate Synthesis of Phosphoglyceride-Linked Enterobacterial Common Antigen

The Gram-negative cell envelope is a complex structure delineating the cell from its environment. Recently, we found that enterobacterial common antigen (ECA) plays a role maintaining the outer membrane (OM) permeability barrier, which excludes toxic molecules including many antibiotics. ECA is a conserved carbohydrate found throughout Enterobacterales (e.g., Salmonella, Klebsiella, and Yersinia). There are two OM forms of ECA (phosphoglyceride-linked ECA_PG and lipopolysaccharide-linked ECA_LPS) and one periplasmic form of ECA (cyclic ECA_CYC). ECA_PG, found in the outer leaflet of the OM, consists of a linear ECA oligomer attached to phosphoglyceride through a phosphodiester linkage. The process through which ECA_PG is produced from polymerized ECA is unknown. Therefore, we set out to identify genes interacting genetically with ECA_PG biosynthesis in Escherichia coli K-12 using the competition between ECA and peptidoglycan biosynthesis. Through transposon-directed insertion sequencing, we identified an interaction between elyC and ECA_PG biosynthesis. ElyC is an inner membrane protein previously shown to alter peptidoglycan biosynthesis rates. We found ΔelyC was lethal specifically in strains producing ECA_PG without other ECA forms, suggesting ECA_PG biosynthesis impairment or dysregulation. Further characterization suggested ElyC inhibits ECA_PG synthesis in a posttranscriptional manner. Moreover, the full impact of ElyC on ECA levels requires the presence of ECA_CYC. Our data demonstrate ECA_CYC can regulate ECA_PG synthesis in strains wild type for elyC. Overall, our data demonstrate ElyC and ECA_CYC act in a novel pathway that regulates the production of ECA_PG, supporting a model in which ElyC provides feedback regulation of ECA_PG production based on the periplasmic levels of ECA_CYC.

Bioactive Antimicrobial Peptides as Therapeutic Agents for Infected Diabetic Foot Ulcers

Diabetic foot ulcer (DFU) is a devastating complication, affecting around 15% of diabetic patients and representing a leading cause of non-traumatic amputations. Notably, the risk of mixed bacterial–fungal infection is elevated and highly associated with wound necrosis and poor clinical outcomes. However, it is often underestimated in the literature. Therefore, polymicrobial infection control must be considered for effective management of DFU. It is noteworthy that antimicrobial resistance is constantly rising overtime, therefore increasing the need for new alternatives to antibiotics and antifungals. Antimicrobial peptides (AMPs) are endogenous peptides that are naturally abundant in several organisms, such as bacteria, amphibians and mammals, particularly in the skin. These molecules have shown broad-spectrum antimicrobial activity and some of them even have wound-healing activity, establishing themselves as ideal candidates for treating multi-kingdom infected wounds. Furthermore, the role of AMPs with antifungal activity in wound management is poorly described and deserves further investigation in association with antibacterial agents, such as antibiotics and AMPs with antibacterial activity, or alternatively the application of broad-spectrum antimicrobial agents that target both aerobic and anaerobic bacteria, as well as fungi. Accordingly, the aim of this review is to unravel the molecular mechanisms by which AMPs achieve their dual antimicrobial and wound-healing properties, and to discuss how these are currently being applied as promising therapies against polymicrobial-infected chronic wounds such as DFUs.

Peptidomimetic analogues of an Arg-Trp-x-x-Trp motif responsible for interaction of translocase MraY with bacteriophage ϕX174 lysis protein E

Translocase MraY is the target for bacteriophage ϕX174 lysis protein E, which interacts via a protein-protein interaction mediated by Phe-288 and Glu-287 of E. coli MraY, and an Arg-Trp-x-x-Trp motif on protein E, also found in several cationic antimicrobial peptides. Analogues of Arg-Trp-octyl ester, found previously to show antimicrobial activity, were tested for antimicrobial activity, with Lys-Trp-oct (MIC₅₀P. fluorescens 5 µg/mL) and Arg-Trp-decyl ester (MIC₅₀P. fluorescens 3 µg/mL) showing enhanced antimicrobial activity. Synthesis and testing of α-helix peptidomimetic analogues for this motif revealed improved antibacterial activity (MIC₅₀E. coli 4-7 µg/mL) for analogues containing two aromatic substituents, mimicking the Arg-Trp-x-x-Trp motif, and MraY inhibition (IC₅₀ 140 µM) by one such peptidomimetic. Investigation of mechanism of action using the Alamar Blue membrane permeabilisation assay revealed bacteriostatic and bacteriocidal mechanisms in different members of this set of compounds, raising the possibility of more than one biological target. The observed antimicrobial activity and MraY inhibition shown by peptidomimetic compounds confirms that this site could be targeted by drug-like molecules.

Head and Neck Squamous Cell Carcinoma: Risk Factors, Molecular Alterations, Immunology and Peptide Vaccines

Head and neck squamous cell carcinoma (HNSCC) arises from the epithelial lining of the oral cavity, hypopharynx, oropharynx, and larynx. There are several potential risk factors that cause the generation of HNSCC, including cigarette smoking, alcohol consumption, betel quid chewing, inadequate nutrition, poor oral hygiene, HPV and Epstein–Barr virus, and Candida albicans infections. HNSCC has causative links to both environmental factors and genetic mutations, with the latter playing a more critical role in cancer progression. These molecular changes to epithelial cells include the inactivation of cancer suppressor genes and proto-oncogenes overexpression, resulting in tumour cell proliferation and distant metastasis. HNSCC patients have impaired dendritic cell (DC) and natural killer (NK) cell functions, increased production of higher immune-suppressive molecules, loss of regulatory T cells and co-stimulatory molecules and major histocompatibility complex (MHC) class Ι molecules, lower number of lymphocyte subsets, and a poor response to antigen-presenting cells. At present, the standard treatment modalities for HNSCC patients include surgery, chemotherapy and radiotherapy, and combinatorial therapy. Despite advances in the development of novel treatment modalities over the last few decades, survival rates of HNSCC patients have not increased. To establish effective immunotherapies, a greater understanding of interactions between the immune system and HNSCC is required, and there is a particular need to develop novel therapeutic options. A therapeutic cancer vaccine has been proposed as a promising method to improve outcome by inducing a powerful adaptive immune response that leads to cancer cell elimination. Compared with other vaccines, peptide cancer vaccines are more robust and specific. In the past few years, there have been remarkable achievements in peptide-based vaccines for HNSCC patients. Here, we summarize the latest molecular alterations in HNSCC, explore the immune response to HNSCC, and discuss the latest developments in peptide-based cancer vaccine strategies. This review highlights areas for valuable future research focusing on peptide-based cancer vaccines.

Stapled Anoplin as an Antibacterial Agent

Anoplin is a linear 10-amino acid amphipathic peptide (Gly-Leu-Leu-Lys-Arg-Ile-Lys-Thr-Leu-Leu-NH2 ) derived from the venom sac of the solitary wasp. It has broad antimicrobial activity, including an antibacterial one. However, the inhibition of bacterial growth requires several dozen micromolar concentrations of this peptide. Anoplin is positively charged and directly interacts with anionic biological membranes forming an α-helix that disrupts the lipid bilayer. To improve the bactericidal properties of anoplin by stabilizing its helical structure, we designed and synthesized its analogs with hydrocarbon staples. The staple was introduced at two locations resulting in different charges and amphipathicity of the analogs. Circular dichroism studies showed that all modified anoplins adopted an α-helical conformation, both in the buffer and in the presence of membrane mimics. As the helicity of the stapled anoplins increased, their stability in trypsin solution improved. Using the propidium iodide uptake assay in Escherichia coli and Staphylococcus aureus, we confirmed the bacterial membrane disruption by the stapled anoplins. Next, we tested the antimicrobial activity of peptides on a range of Gram-negative and Gram-positive bacteria. Finally, we evaluated peptide hemolytic activity on sheep erythrocytes and cytotoxicity on human embryonic kidney 293 cells. All analogs showed higher antimicrobial activity than unmodified anoplin. Depending on the position of the staple, the peptides were more effective either against Gram-negative or Gram-positive bacteria. Anoplin[5-9], with a lower positive charge and increased hydrophobicity, had higher activity against Gram-positive bacteria but also showed hemolytic and destructive effects on eukaryotic cells. Contrary, anoplin[2-6] with a similar charge and amphipathicity as natural anoplin effectively killed Gram-negative bacteria, also pathogenic drug-resistant strains, without being hemolytic and toxic to eukaryotic cells. Our results showed that anoplin charge, amphipathicity, and location of hydrophobic residues affect the peptide destructive activity on the cell wall, and thus, its antibacterial activity. This means that by manipulating the charge and position of the staple in the sequence, one can manipulate the antimicrobial activity.

Evaluation of Three Antimicrobial Peptides Mixtures to Control the Phytopathogen Responsible for Fire Blight Disease

Fire blight is a severe bacterial plant disease that affects important chain-of-value fruit trees such as pear and apple trees. This disease is caused by Erwinia amylovora, a quarantine phytopathogenic bacterium, which, although highly distributed worldwide, still lacks efficient control measures. The green revolution paradigm demands sustainable agriculture practices, for which antimicrobial peptides (AMPs) have recently caught much attention. The goal of this work was to disclose the bioactivity of three peptides mixtures (BP100:RW-BP100, BP100:CA-M, and RW-BP100:CA-M), against three strains of E. amylovora representing distinct genotypes and virulence (LMG 2024, Ea 630 and Ea 680). The three AMPs' mixtures were assayed at eight different equimolar concentrations ranging from 0.25 to 6 μM (1:1). Results showed MIC and MBC values between 2.5 and 4 μM for every AMP mixture and strain. Regarding cell viability, flow cytometry and alamarBlue reduction, showed high reduction (>25%) of viable cells after 30 min of AMP exposure, depending on the peptide mixture and strain assayed. Hypersensitive response in tobacco plants showed that the most efficient AMPs mixtures and concentrations caused low to no reaction of the plant. Altogether, the AMPs mixtures studied are better treatment solutions to control fire blight disease than the same AMPs applied individually.

dbAMP 2.0: updated resource for antimicrobial peptides with an enhanced scanning method for genomic and proteomic data

The last 18 months, or more, have seen a profound shift in our global experience, with many of us navigating a once-in-100-year pandemic. To date, COVID-19 remains a life-threatening pandemic with little to no targeted therapeutic recourse. The discovery of novel antiviral agents, such as vaccines and drugs, can provide therapeutic solutions to save human beings from severe infections; however, there is no specifically effective antiviral treatment confirmed for now. Thus, great attention has been paid to the use of natural or artificial antimicrobial peptides (AMPs) as these compounds are widely regarded as promising solutions for the treatment of harmful microorganisms. Given the biological significance of AMPs, it was obvious that there was a significant need for a single platform for identifying and engaging with AMP data. This led to the creation of the dbAMP platform that provides comprehensive information about AMPs and facilitates their investigation and analysis. To date, the dbAMP has accumulated 26 447 AMPs and 2262 antimicrobial proteins from 3044 organisms using both database integration and manual curation of >4579 articles. In addition, dbAMP facilitates the evaluation of AMP structures using I-TASSER for automated protein structure prediction and structure-based functional annotation, providing predictive structure information for clinical drug development. Next-generation sequencing (NGS) and third-generation sequencing have been applied to generate large-scale sequencing reads from various environments, enabling greatly improved analysis of genome structure. In this update, we launch an efficient online tool that can effectively identify AMPs from genome/metagenome and proteome data of all species in a short period. In conclusion, these improvements promote the dbAMP as one of the most abundant and comprehensively annotated resources for AMPs. The updated dbAMP is now freely accessible at http://awi.cuhk.edu.cn/dbAMP.

Cationic Antimicrobial Peptides Are Leading the Way to Combat Oropathogenic Infections

Oral dental infections are one of the most common diseases affecting humans, with caries and periodontal disease having the highest incidence. Caries and periodontal disease arise from infections caused by oral bacterial pathogens. Current misuse and overuse of antibiotic treatments have led to the development of antimicrobial resistance. However, recent studies have shown that cationic antimicrobial peptides are a promising family of antibacterial agents that are active against oral pathogenic bacteria and also possess less propensity for development of antimicrobial resistance. This timely Review has a focus on two primary subjects: (i) the oral bacterial pathogens associated with dental infections and (ii) the current development of antimicrobial peptides targeting oral pathogens.

Advances on chemically modified antimicrobial peptides for generating peptide antibiotics

Antimicrobial peptides (AMPs) are pinpointed as promising molecules against antibiotic-resistant bacterial infections. Nevertheless, there is a discrepancy between the AMP sequences generated and the tangible outcomes in clinical trials. AMPs' limitations include enzymatic degradation, chemical/physical instability and toxicity toward healthy human cells. These factors compromise AMPs' bioavailability, resulting in limited therapeutic potential. To overcome such obstacles, peptidomimetic approaches, including glycosylation, PEGylation, lipidation, cyclization, grafting, D-amino acid insertion, stapling and dendrimers are promising strategies to fine-tune AMPs. Here we focused on chemical modifications applied for AMP optimization and how they have helped these peptide-based antibiotic candidates' design and translational potential.

Current Advances in Lipid and Polymeric Antimicrobial Peptide Delivery Systems and Coatings for the Prevention and Treatment of Bacterial Infections

Bacterial infections constitute a threat to public health as antibiotics are becoming less effective due to the emergence of antimicrobial resistant strains and biofilm and persister formation. Antimicrobial peptides (AMPs) are considered excellent alternatives to antibiotics; however, they suffer from limitations related to their peptidic nature and possible toxicity. The present review critically evaluates the chemical characteristics and antibacterial effects of lipid and polymeric AMP delivery systems and coatings that offer the promise of enhancing the efficacy of AMPs, reducing their limitations and prolonging their half-life. Unfortunately, the antibacterial activities of these systems and coatings have mainly been evaluated in vitro against planktonic bacteria in less biologically relevant conditions, with only some studies focusing on the antibiofilm activities of the formulated AMPs and on the antibacterial effects in animal models. Further improvements of lipid and polymeric AMP delivery systems and coatings may involve the functionalization of these systems to better target the infections and an analysis of the antibacterial activities in biologically relevant environments. Based on the available data we proposed which polymeric AMP delivery system or coatings could be profitable for the treatment of the different hard-to-treat infections, such as bloodstream infections and catheter- or implant-related infections.

Host Defense Peptide-Mimicking Polymers and Polymeric-Brush-Tethered Host Defense Peptides: Recent Developments, Limitations, and Potential Success

Amphiphilic antimicrobial polymers have attracted considerable interest as structural mimics of host defense peptides (HDPs) that provide a broad spectrum of activity and do not induce bacterial-drug resistance. Likewise, surface engineered polymeric-brush-tethered HDP is considered a promising coating strategy that prevents infections and endows implantable materials and medical devices with antifouling and antibacterial properties. While each strategy takes a different approach, both aim to circumvent limitations of HDPs, enhance physicochemical properties, therapeutic performance, and enable solutions to unmet therapeutic needs. In this review, we discuss the recent advances in each approach, spotlight the fundamental principles, describe current developments with examples, discuss benefits and limitations, and highlight potential success. The review intends to summarize our knowledge in this research area and stimulate further work on antimicrobial polymers and functionalized polymeric biomaterials as strategies to fight infectious diseases.

Mechanistic Understanding from Molecular Dynamics in Pharmaceutical Research 2: Lipid Membrane in Drug Design

We review the use of molecular dynamics (MD) simulation as a drug design tool in the context of the role that the lipid membrane can play in drug action, i.e., the interaction between candidate drug molecules and lipid membranes. In the standard "lock and key" paradigm, only the interaction between the drug and a specific active site of a specific protein is considered; the environment in which the drug acts is, from a biophysical perspective, far more complex than this. The possible mechanisms though which a drug can be designed to tinker with physiological processes are significantly broader than merely fitting to a single active site of a single protein. In this paper, we focus on the role of the lipid membrane, arguably the most important element outside the proteins themselves, as a case study. We discuss work that has been carried out, using MD simulation, concerning the transfection of drugs through membranes that act as biological barriers in the path of the drugs, the behavior of drug molecules within membranes, how their collective behavior can affect the structure and properties of the membrane and, finally, the role lipid membranes, to which the vast majority of drug target proteins are associated, can play in mediating the interaction between drug and target protein. This review paper is the second in a two-part series covering MD simulation as a tool in pharmaceutical research; both are designed as pedagogical review papers aimed at both pharmaceutical scientists interested in exploring how the tool of MD simulation can be applied to their research and computational scientists interested in exploring the possibility of a pharmaceutical context for their research.

The emergence of the C-H functionalization strategy in medicinal chemistry and drug discovery

Owing to the market competitiveness and urgent societal need, an optimum speed of drug discovery is an important criterion for successful implementation. Despite the rapid ascent of artificial intelligence and computational and bioanalytical techniques to accelerate drug discovery in big pharma, organic synthesis of privileged scaffolds predicted in silico for in vitro and in vivo studies is still considered as the rate-limiting step. C-H activation is the latest technology added into an organic chemist's toolbox for the rapid construction and late-stage modification of functional molecules to achieve the desired chemical and physical properties. Particularly, elimination of prefunctionalization steps, exceptional functional group tolerance, complexity-to-diversity oriented synthesis, and late-stage functionalization of privileged medicinal scaffolds expand the chemical space. It has immense potential for the rapid synthesis of a library of molecules, structural modification to achieve the required pharmacological properties such as absorption, distribution, metabolism, excretion, toxicology (ADMET) and attachment of chemical reporters for proteome profiling, metabolite synthesis, etc. for preclinical studies. Although heterocycle synthesis, late-stage drug modification, ¹⁸F labelling, methylation, etc. via C-H functionalization have been reviewed from the synthetic standpoint, a general overview of these protocols from medicinal and drug discovery aspects has not been reviewed. In this feature article, we will discuss the recent trends of C-H activation methodologies such as synthesis of medicinal scaffolds through C-H activation/annulation cascade; C-H arylation for sp²-sp² and sp²-sp³ cross-coupling; C-H borylation/silylation to introduce a functional linchpin for further manipulation; C-H amination for N-heterocycles and hydrogen bond acceptors; C-H fluorination/fluoroalkylation to tune polarity and lipophilicity; C-H methylation: methyl magic in drug discovery; peptide modification and macrocyclization for therapeutics and biologics; fluorescent labelling and radiolabelling for bioimaging; bioconjugation for chemical biology studies; drug-metabolite synthesis for biodistribution and excretion studies; late-stage diversification of drug-molecules to increase efficacy and safety; cutting-edge DNA encoded library synthesis and improved synthesis of drug molecules via C-H activation in medicinal chemistry and drug discovery.

Bacillus amyloliquefaciens-Derived Lipopeptide Biosurfactants Inhibit Biofilm Formation and Expression of Biofilm-Related Genes of Staphylococcus aureus

Biosurfactants (BSs) are surface-active compounds produced by diverse microorganisms, including the genus Bacillus. These bioactive compounds possess biological activities such as antiadhesive, antimicrobial and antibiofilm effects that can lead to important applications in combating many infections. Based on these findings, we decided to investigate the antibiofilm activity of BSs from the marine Bacillus amyloliquefaciens against Staphylococcus aureus CCM 4223. Expression of biofilm-related genes was also evaluated using qRT-PCR. Isolated and partially purified BSs were identified and characterized by molecular tools and by UHPLC-DAD and MALDI-TOF/MS. Bacillus amyloliquefaciens 3/22, that exhibited surfactant activity evaluated by oil spreading assay, was characterized using the 16S rRNA sequencing method. Screening by PCR detected the presence of the sfp, srfAA, fenD and ituD genes, suggesting production of the lipopeptides (LPs) surfactin, fengycin and iturin. The above findings were further supported by the results of UHPLC-DAD and MALDI-TOF/MS. As quantified by the crystal violet method, the LPs significantly (p < 0.001) reduced biofilm formation of S. aureus in a dose-dependent manner and decreased expression of biofilm-related genes fnbA, fnbB, sortaseA and icaADBC operon. Data from our investigation indicate a promising therapeutic application for LPs isolated from B. amyloliquefaciens toward prevention of S. aureus biofilm infections.

The Era of Antimicrobial Peptides: Use of Hepcidins to Prevent or Treat Bacterial Infections and Iron Disorders

The current treatments applied in aquaculture to limit disease dissemination are mostly based on the use of antibiotics, either as prophylactic or therapeutic agents, with vaccines being available for a limited number of fish species and pathogens. Antimicrobial peptides are considered as promising novel substances to be used in aquaculture, due to their antimicrobial and immunomodulatory activities. Hepcidin, the major iron metabolism regulator, is found as a single gene in most mammals, but in certain fish species, including the European sea bass (Dicentrarchus labrax), two different hepcidin types are found, with specialized roles: the single type 1 hepcidin is involved in iron homeostasis trough the regulation of ferroportin, the only known iron exporter; and the various type 2 hepcidins present antimicrobial activity against a number of different pathogens. In this study, we tested the administration of sea bass derived hepcidins in models of infection and iron overload. Administration with hamp2 substantially reduced fish mortalities and bacterial loads, presenting itself as a viable alternative to the use of antibiotics. On the other hand, hamp1 seems to attenuate the effects of iron overload. Further studies are necessary to test the potential protective effects of hamp2 against other pathogens, as well as to understand how hamp2 stimulate the inflammatory responses, leading to an increased fish survival upon infection.

Butyrate, Forskolin, and Lactose Synergistically Enhance Disease Resistance by Inducing the Expression of the Genes Involved in Innate Host Defense and Barrier Function

The rising concern of antimicrobial resistance highlights a need for effective alternatives to antibiotics for livestock production. Butyrate, forskolin, and lactose are three natural products known to induce the synthesis of host defense peptides (HDP), which are a critical component of innate immunity. In this study, the synergy among butyrate, forskolin, and lactose in enhancing innate host defense, barrier function, and resistance to necrotic enteritis and coccidiosis was investigated. Our results indicated that the three compounds synergistically augmented the expressions of multiple HDP and barrier function genes in chicken HD11 macrophages. The compounds also showed an obvious synergy in promoting HDP gene expressions in chicken jejunal explants. Dietary supplementation of a combination of 1 g/kg sodium butyrate, 10 mg/kg forskolin-containing plant extract, and 10 g/kg lactose dramatically improved the survival of chickens from 39% to 94% (p < 0.001) in a co-infection model of necrotic enteritis. Furthermore, the three compounds largely reversed growth suppression, significantly alleviated intestinal lesions, and reduced colonization of Clostridium perfringens or Eimeria maxima in chickens with necrotic enteritis and coccidiosis (p < 0.01). Collectively, dietary supplementation of butyrate, forskolin, and lactose is a promising antibiotic alternative approach to disease control and prevention for poultry and possibly other livestock species.

Production and Purification of Two Bioactive Antimicrobial Peptides Using a Two-Step Approach Involving an Elastin-Like Fusion Tag

Antimicrobial resistance is an increasing global threat, demanding new therapeutic biomolecules against multidrug-resistant bacteria. Antimicrobial peptides (AMPs) are promising candidates for a new generation of antibiotics, but their potential application is still in its infancy, mostly due to limitations associated with large-scale production. The use of recombinant DNA technology for the production of AMPs fused with polymer tags presents the advantage of high-yield production and cost-efficient purification processes at high recovery rates. Owing to their unique properties, we explored the use of an elastin-like recombinamer (ELR) as a fusion partner for the production and isolation of two different AMPs (ABP-CM4 and Synoeca-MP), with an interspacing formic acid cleavage site. Recombinant AMP-ELR proteins were overproduced in Escherichia coli and efficiently purified by temperature cycles. The introduction of a formic acid cleavage site allowed the isolation of AMPs, resorting to a two-step methodology involving temperature cycles and a simple size-exclusion purification step. This simple and easy-to-implement purification method was demonstrated to result in high recovery rates of bioactive AMPs. The minimum inhibitory concentration (MIC) of the free AMPs was determined against seven different bacteria of clinical relevance (Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and two Burkholderia cenocepacia strains), in accordance with the EUCAST/CLSI antimicrobial susceptibility testing standards. All the bacterial strains (except for Pseudomonas aeruginosa) were demonstrated to be susceptible to ABP-CM4, including a resistant Burkholderia cenocepacia clinical strain. As for Synoeca-MP, although it did not inhibit the growth of Pseudomonas aeruginosa or Klebsiella pneumoniae, it was demonstrated to be highly active against the remaining bacteria. The present work provides the basis for the development of an efficient and up-scalable biotechnological platform for the production and purification of active AMPs against clinically relevant bacteria.

Antimicrobial peptides: mechanism of action, activity and clinical potential

The management of bacterial infections is becoming a major clinical challenge due to the rapid evolution of antibiotic resistant bacteria. As an excellent candidate to overcome antibiotic resistance, antimicrobial peptides (AMPs) that are produced from the synthetic and natural sources demonstrate a broad-spectrum antimicrobial activity with the high specificity and low toxicity. These peptides possess distinctive structures and functions by employing sophisticated mechanisms of action. This comprehensive review provides a broad overview of AMPs from the origin, structural characteristics, mechanisms of action, biological activities to clinical applications. We finally discuss the strategies to optimize and develop AMP-based treatment as the potential antimicrobial and anticancer therapeutics.

Anti-biofilm and anti-inflammatory effects of Lycosin-II isolated from spiders against multi-drug resistant bacteria

Currently, multidrug-resistant bacteria are rapidly increasing worldwide because of the misuse or overuse of antibiotics. In particular, few options exist for treating infections caused by long-persisting oxacillin-resistant strains and recently proliferating carbapenem-resistant strains. Therefore, alternative treatments are urgently needed. The antimicrobial peptide (AMP) Lycosin-II is a peptide consisting of 21 amino acids isolated from the venom of the spider Lycosa singoriensis. Lycosin-II showed strong antibacterial activity and biofilm inhibition effects against gram-positive and gram-negative bacteria including oxacillin-resistant Staphylococcus aureus (S. aureus) and meropenem-resistant Pseudomonas aeruginosa (P. aeruginosa) isolated from patients. In addition, Lycosin-II was not cytotoxic against human foreskin fibroblast Hs27 or hemolytic against sheep red blood cells at the concentration of which exerted antibacterial activity. The mechanism of action of Lycosin-II involves binding to lipoteichoic acid and lipopolysaccharide of gram-positive and gram-negative bacterial membranes, respectively, to destroy the bacterial membrane. Moreover, Lycosin-II showed anti-inflammatory effects by inhibiting the expression of pro-inflammatory cytokines that are increased during bacterial infection in Hs27 cells. These results suggest that Lycosin-II can serve as a therapeutic agent against infections with multidrug-resistant strains.

A Method for Rapid Screening, Expression, and Purification of Antimicrobial Peptides

In this study, a method for the rapid screening, expression and purification of antimicrobial peptides (AMPs) was developed. AMP genes were fused to a heat-resistant CL7 tag using the SLOPE method, and cloned into Escherichia coli and Pichia pastoris expression vectors. Twenty E. coli and ten P. pastoris expression vectors were constructed. Expression supernatants were heated, heteroproteins were removed, and fusion proteins were purified by nickel affinity (Ni-NTA) chromatography. Fusion proteins were digested on the column using human rhinovirus (HRV) 3C protease, and AMPs were released and further purified. Five AMPs (1, 2, 6, 13, 16) were purified using the E. coli expression system, and one AMP (13) was purified using the P. pastoris expression system. Inhibition zone and minimum inhibitory concentration (MIC) tests confirmed that one P. pastoris⌐-derived and two E. coli-derived AMPs have the inhibition activity. The MIC of AMP 13 and 16 from E. coli was 24.2 μM, and the MIC of AMP 13 from P. pastoris was 8.1 μM. The combination of prokaryotic and eukaryotic expression systems expands the universality of the developed method, facilitating screening of a large number of biologically active AMPs, establishing an AMP library, and producing AMPs by industrialised biological methods.

Design, Synthesis and Antifungal Activity of Stapled Aurein1.2 Peptides

Aurein1.2 is a 13-residue antimicrobial peptide secreted by the Australian tree frog Litoria aurea. In order to improve its stabilities, the helical contents and corresponding biological activities of Aurein1.2 (a series of stapled analogues) were synthesized, and their potential antifungal activities were evaluated. Not surprisingly, the stapled Aurein1.2 peptides showed higher proteolytic stability and helicity than the linear counterpart. The minimum inhibitory concentration (MIC) of ten stapled peptides against six strains of common pathogenic fungi was determined by the microscale broth dilution method recommended by CLSI. Of them, Sau-1, Sau-2, Sau-5, and Sau-9 exhibited better inhibitory effects on the fungi than the linear peptide. These stapled Aurein1.2 peptides may serve as the leading compounds for further optimization and antifungal therapy.

Molecular engineering of antimicrobial peptide (AMP)-polymer conjugates

As antimicrobial resistance becomes an increasing threat, bringing significant economic and health burdens, innovative antimicrobial treatments are urgently needed. While antimicrobial peptides (AMPs) are promising therapeutics, exhibiting high activity against resistant bacterial strains, limited stability and toxicity to mammalian cells has hindered clinical development. Attaching AMPs to polymers provides opportunities to present AMPs in a way that maximizes bacterial killing while enhancing compatibility with mammalian cells, stability, and solubility. Conjugation of an AMP to a linear hydrophilic polymer yields the desired improvements in stability, mammalian cell compatibility, and solubility, yet often markedly reduces bactericidal effects. Non-linear polymer architectures and supramolecular assemblies that accommodate multiple AMPs per polymer chain afford AMP-polymer conjugates that strike a superior balance of antimicrobial activity, mammalian cell compatibility, stability, and solubility. Therefore, we review the design criteria, building blocks, and synthetic strategies for engineering AMP-polymer conjugates, emphasizing the connection between molecular architecture and antimicrobial performance to inspire and enable further innovation to advance this emerging class of biomaterials.

Antimicrobial Peptide Modifications against Clinically Isolated Antibiotic-Resistant Salmonella

Antimicrobial peptides are promising molecules to address the global antibiotic resistance problem, however, optimization to achieve favorable potency and safety is required. Here, a peptide-template modification approach was employed to design physicochemical variants based on net charge, hydrophobicity, enantiomer, and terminal group. All variants of the scorpion venom peptide BmKn-2 with amphipathic α-helical cationic structure exhibited an increased antibacterial potency when evaluated against multidrug-resistant Salmonella isolates at a MIC range of 4–8 µM. They revealed antibiofilm activity in a dose-dependent manner. Sheep red blood cells were used to evaluate hemolytic and cell selectivity properties. Peptide Kn2-5R-NH₂, dKn2-5R-NH₂, and 2F-Kn2-5R-NH₂ (variants with +6 charges carrying amidated C-terminus) showed stronger antibacterial activity than Kn2-5R (a variant with +5 charges bearing free-carboxyl group at C-terminus). Peptide dKn2-5R-NH₂ (d-enantiomer) exhibited slightly weaker antibacterial activity with much less hemolytic activity (higher hemolytic concentration 50) than Kn2-5R-NH₂ (l-enantiomer). Furthermore, peptide Kn2-5R with the least hydrophobicity had the lowest hemolytic activity and showed the highest specificity to Salmonella (the highest selectivity index). This study also explained the relationship of peptide physicochemical properties and bioactivities that would fulfill and accelerate progress in peptide antibiotic research and development.

Effects of Lipidation on a Proline-Rich Antibacterial Peptide

The emergence of multidrug-resistant bacteria is a worldwide health problem. Antimicrobial peptides have been recognized as potential alternatives to conventional antibiotics, but still require optimization. The proline-rich antimicrobial peptide Bac7(1-16) is active against only a limited number of Gram-negative bacteria. It kills bacteria by inhibiting protein synthesis after its internalization, which is mainly supported by the bacterial transporter SbmA. In this study, we tested two different lipidated forms of Bac7(1-16) with the aim of extending its activity against those bacterial species that lack SbmA. We linked a C12-alkyl chain or an ultrashort cationic lipopeptide Lp-I to the C-terminus of Bac7(1-16). Both the lipidated Bac-C12 and Bac-Lp-I forms acquired activity at low micromolar MIC values against several Gram-positive and Gram-negative bacteria. Moreover, unlike Bac7(1-16), Bac-C12, and Bac-Lp-I did not select resistant mutants in E. coli after 14 times of exposure to sub-MIC concentrations of the respective peptide. We demonstrated that the extended spectrum of activity and absence of de novo resistance are likely related to the acquired capability of the peptides to permeabilize cell membranes. These results indicate that C-terminal lipidation of a short proline-rich peptide profoundly alters its function and mode of action and provides useful insights into the design of novel broad-spectrum antibacterial agents.

Long-Lasting Stable Expression of Human LL-37 Antimicrobial Peptide in Transgenic Barley Plants

Antimicrobial peptides play a crucial role in the innate immune system of multicellular organisms. LL-37 is the only known member of the human cathelicidin family. As well as possessing antibacterial properties, it is actively involved in various physiological responses in eukaryotic cells. Accordingly, there is considerable interest in large-scale, low-cost, and microbial endotoxin-free production of LL-37 recombinant peptides for pharmaceutical applications. As a heterologous expression biofactory, we have previously obtained homologous barley (Hordeum vulgare L.) as an attractive vehicle for producing recombinant human LL-37 in the grain storage compartment, endosperm. The long-term stability of expression and inheritance of transgenes is necessary for the successful commercialization of recombinant proteins. Here, we report the stable inheritance and expression of the LL-37 gene in barley after six generations, including two consecutive seasons of experimental field cultivation. The transgenic plants showed normal growth and remained fertile. Based on the bacteria viability test, the produced peptide LL-37 retained high antibacterial activity.

Antibacterial Peptides Produced by Alcalase from Cowpea Seed Proteins

Cowpea seed protein hydrolysates (CPH) were output from cowpea seeds applying alcalase® from Bacillus licheniformis. CPH with an elevated level of hydrolysis was fractionated by size exclusion chromatography (SEC). Both CPH and SEC-portions showed to contain antimicrobial peptides (AMPs) as they inhibited both Gram-positive bacteria, such as Listeria monocytogenes LMG10470 (L. monocytogenes), Listeria innocua. LMG11387 (L. innocua), Staphylococcus aureus ATCC25923 (S.aureus), and Streptococcus pyogenes ATCC19615 (St.pyogenes), and Gram-negative bacteria, such as Klebsiella pnemoniae ATCC43816 (K. pnemoniae), Pseudomonas aeroginosa ATCC26853 (P. aeroginosa), Escherichia coli ATCC25468) (E.coli) and Salmonella typhimurium ATCC14028 (S. typhimurium).The data exhibited that both CPH and size exclusion chromatography-fraction 1 (SEC-F1) showed high antibacterial efficiency versus almost all the assessed bacteria. The MIC of the AMPs within SEC-F1 and CPHs were (25 µg/mL) against P. aeruginosa, E.coli and St. pyogenes. However, higher MICsof approximately 100-150 µg/mL showed for both CPHs and SEC-F1 against both S. aureus and L. innocua; it was 50 µg/mL of CPH against S.aureus. The Electro-spray-ionization-mass-spectrometry (ESI-MS) of fraction (1) revealed 10 dipeptides with a molecular masses arranged from 184 Da to 364 Da and one Penta peptide with a molecular mass of approximately 659 Da inthe case of positive ions. While the negative ions showed 4 dipeptides with the molecular masses that arranged from 330 Da to 373 Da. Transmission electron microscope (TEM) demonstrated that the SEC-F1 induced changes in the bacterial cells affected. Thus, the results suggested that the hydrolysis of cowpea seed proteins by Alcalase is an uncomplicated appliance to intensify its antibacterial efficiency.

PhytoAFP: In Silico Approaches for Designing Plant-Derived Antifungal Peptides

Emerging infectious diseases (EID) are serious problems caused by fungi in humans and plant species. They are a severe threat to food security worldwide. In our current work, we have developed a support vector machine (SVM)-based model that attempts to design and predict therapeutic plant-derived antifungal peptides (PhytoAFP). The residue composition analysis shows the preference of C, G, K, R, and S amino acids. Position preference analysis shows that residues G, K, R, and A dominate the N-terminal. Similarly, residues N, S, C, and G prefer the C-terminal. Motif analysis reveals the presence of motifs like NYVF, NYVFP, YVFP, NYVFPA, and VFPA. We have developed two models using various input functions such as mono-, di-, and tripeptide composition, as well as binary, hybrid, and physiochemical properties, based on methods that are applied to the main data set. The TPC-based monopeptide composition model achieved more accuracy, 94.4%, with a Matthews correlation coefficient (MCC) of 0.89. Correspondingly, the second-best model based on dipeptides achieved an accuracy of 94.28% under the MCC 0.89 of the training dataset.

Immunomodulatory Properties of Host Defence Peptides in Skin Wound Healing

Cutaneous wound healing is a vital biological process that aids skin regeneration upon injury. Wound healing failure results from persistent inflammatory conditions observed in diabetes, or autoimmune diseases like psoriasis. Chronic wounds are incurable due to factors like poor oxygenation, aberrant function of peripheral sensory nervature, inadequate nutrients and blood tissue supply. The most significant hallmark of chronic wounds is heavily aberrant immune skin function. The immune response in humans relies on a large network of signalling molecules and their interactions. Research studies have reported on the dual role of host defence peptides (HDPs), which are also often called antimicrobial peptides (AMPs). Their duality reflects their potential for acting as antibacterial peptides, and as immunodulators that assist in modulating several biological signalling pathways related to processes such as wound healing, autoimmune disease, and others. HDPs may differentially control gene regulation and alter the behaviour of epithelial and immune cells, resulting in modulation of immune responses. In this review, we shed light on the understanding and most recent advances related to molecular mechanisms and immune modulatory features of host defence peptides in human skin wound healing. Understanding their functional role in skin immunity may further inspire topical treatments for chronic wounds.

Microfluidic Tools for Enhanced Characterization of Therapeutic Stem Cells and Prediction of Their Potential Antimicrobial Secretome

Antibiotic resistance is creating enormous attention on the development of new antibiotic-free therapy strategies for bacterial diseases. Mesenchymal stromal stem cells (MSCs) are the most promising candidates in current clinical trials and included in several cell-therapy protocols. Together with the well-known immunomodulatory and regenerative potential of the MSC secretome, these cells have shown direct and indirect anti-bacterial effects. However, the low reproducibility and standardization of MSCs from different sources are the current limitations prior to the purification of cell-free secreted antimicrobial peptides and exosomes. In order to improve MSC characterization, novel label-free functional tests, evaluating the biophysical properties of the cells, will be advantageous for their cell profiling, population sorting, and quality control. We discuss the potential of emerging microfluidic technologies providing new insights into density, shape, and size of live cells, starting from heterogeneous or 3D cultured samples. The prospective application of these technologies to studying MSC populations may contribute to developing new biopharmaceutical strategies with a view to naturally overcoming bacterial defense mechanisms.

Synergistic effect and antibiofilm activity of an antimicrobial peptide with traditional antibiotics against multi-drug resistant bacteria

Combined treatment of AMPs with classical antibiotics has gained interest because it often results in a synergistic antibacterial effect. We demonstrated here that Pt5-1c, an AMP derived from phosvitin, had antibacterial activity against the MDR bacteria (S. aureus USA500, E. coli 577 and K. pneumoniae 2182) in the presence of serum. On this basis, we showed that Pt5-1c was synergistically active with traditional antibiotics (oxacillin, vancomycin, streptomycin and azithromycin) against the three MDR bacteria growing as biofilms in vitro and in vivo. Moreover, Pt5-1c restored sensitivity of S. aureus USA500 to oxacillin and vancomycin, E. coli 577 to streptomycin and K. pneumoniae 2182 to azithromycin. Importantly, long-term exposure to Pt5-1c did not give rise to antimicrobial resistance. Collectively, these data not only suggest a promising combinatorial therapy strategy to combat antibiotics-tolerant infections but also present a possibility of Pt5-1c being used to prolong the application of antibiotics including oxacillin, vancomycin, streptomycin and azithromycin, that are under threat of becoming ineffective due to antibiotic resistance.